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  <div class="question_difficulty">
   难度：Easy
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  <div>
   <h1 class="question_title">
    160. Intersection of Two Linked Lists
   </h1>
   <p>
    Write a program to find the node at which the intersection of two singly linked lists begins.
   </p>
   <p>
    For example, the following two linked lists:
   </p>
   <a href="https://assets.leetcode.com/uploads/2018/12/13/160_statement.png" target="_blank">
    <img alt="" src="https://assets.leetcode.com/uploads/2018/12/13/160_statement.png" style="margin-top: 10px; margin-bottom: 10px; width: 400px; height: 130px;">
   </a>
   <p>
    begin to intersect at node c1.
   </p>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     Example 1:
    </strong>
   </p>
   <a href="https://assets.leetcode.com/uploads/2018/12/13/160_example_1.png" target="_blank">
    <img alt="" src="https://assets.leetcode.com/uploads/2018/12/13/160_example_1.png" style="margin-top: 10px; margin-bottom: 10px; width: 400px; height: 130px;">
   </a>
   <pre>
<strong>Input: </strong>intersectVal = 8, listA = [4,1,8,4,5], listB = [5,0,1,8,4,5], skipA = 2, skipB = 3
<strong>Output:</strong> Reference of the node with value = 8
<strong>Input Explanation:</strong> The intersected node's value is 8 (note that this must not be 0 if the two lists intersect). From the head of A, it reads as [4,1,8,4,5]. From the head of B, it reads as [5,0,1,8,4,5]. There are 2 nodes before the intersected node in A; There are 3 nodes before the intersected node in B.</pre>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     Example 2:
    </strong>
   </p>
   <a href="https://assets.leetcode.com/uploads/2018/12/13/160_example_2.png" target="_blank">
    <img alt="" src="https://assets.leetcode.com/uploads/2018/12/13/160_example_2.png" style="margin-top: 10px; margin-bottom: 10px; width: 350px; height: 136px;">
   </a>
   <pre>
<strong>Input: </strong>intersectVal&nbsp;= 2, listA = [0,9,1,2,4], listB = [3,2,4], skipA = 3, skipB = 1
<strong>Output:</strong> Reference of the node with value = 2
<strong>Input Explanation:</strong>&nbsp;The intersected node's value is 2 (note that this must not be 0 if the two lists intersect). From the head of A, it reads as [0,9,1,2,4]. From the head of B, it reads as [3,2,4]. There are 3 nodes before the intersected node in A; There are 1 node before the intersected node in B.
</pre>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     Example 3:
    </strong>
   </p>
   <a href="https://assets.leetcode.com/uploads/2018/12/13/160_example_3.png" target="_blank">
    <img alt="" src="https://assets.leetcode.com/uploads/2018/12/13/160_example_3.png" style="margin-top: 10px; margin-bottom: 10px; width: 200px; height: 126px;">
   </a>
   <pre>
<strong>Input: </strong>intersectVal = 0, listA = [2,6,4], listB = [1,5], skipA = 3, skipB = 2
<strong>Output:</strong> null
<strong>Input Explanation:</strong> From the head of A, it reads as [2,6,4]. From the head of B, it reads as [1,5]. Since the two lists do not intersect, intersectVal must be 0, while skipA and skipB can be arbitrary values.
<strong>Explanation:</strong> The two lists do not intersect, so return null.
</pre>
   <p>
    &nbsp;
   </p>
   <p>
    <b>
     Notes:
    </b>
   </p>
   <ul>
    <li>
     If the two linked lists have no intersection at all, return
     <code>
      null
     </code>
     .
    </li>
    <li>
     The linked lists must retain their original structure after the function returns.
    </li>
    <li>
     You may assume there are no cycles anywhere in the entire linked structure.
    </li>
    <li>
     Your code should preferably run in O(n) time and use only O(1) memory.
    </li>
   </ul>
  </div>
  <div>
   <h1 class="question_title">
    160. 相交链表
   </h1>
   <p>
    编写一个程序，找到两个单链表相交的起始节点。
   </p>
   <p>
    如下面的两个链表
    <strong>
     ：
    </strong>
   </p>
   <p>
    <a href="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/12/14/160_statement.png" target="_blank">
     <img alt="" src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/12/14/160_statement.png" style="height: 130px; width: 400px;">
    </a>
   </p>
   <p>
    在节点 c1 开始相交。
   </p>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     示例 1：
    </strong>
   </p>
   <p>
    <a href="https://assets.leetcode.com/uploads/2018/12/13/160_example_1.png" target="_blank">
     <img alt="" src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/12/14/160_example_1.png" style="height: 130px; width: 400px;">
    </a>
   </p>
   <pre><strong>输入：</strong>intersectVal = 8, listA = [4,1,8,4,5], listB = [5,0,1,8,4,5], skipA = 2, skipB = 3
<strong>输出：</strong>Reference of the node with value = 8
<strong>输入解释：</strong>相交节点的值为 8 （注意，如果两个列表相交则不能为 0）。从各自的表头开始算起，链表 A 为 [4,1,8,4,5]，链表 B 为 [5,0,1,8,4,5]。在 A 中，相交节点前有 2 个节点；在 B 中，相交节点前有 3 个节点。
</pre>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     示例&nbsp;2：
    </strong>
   </p>
   <p>
    <a href="https://assets.leetcode.com/uploads/2018/12/13/160_example_2.png" target="_blank">
     <img alt="" src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/12/14/160_example_2.png" style="height: 136px; width: 350px;">
    </a>
   </p>
   <pre><strong>输入：</strong>intersectVal&nbsp;= 2, listA = [0,9,1,2,4], listB = [3,2,4], skipA = 3, skipB = 1
<strong>输出：</strong>Reference of the node with value = 2
<strong>输入解释：</strong>相交节点的值为 2 （注意，如果两个列表相交则不能为 0）。从各自的表头开始算起，链表 A 为 [0,9,1,2,4]，链表 B 为 [3,2,4]。在 A 中，相交节点前有 3 个节点；在 B 中，相交节点前有 1 个节点。
</pre>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     示例&nbsp;3：
    </strong>
   </p>
   <p>
    <a href="https://assets.leetcode.com/uploads/2018/12/13/160_example_3.png" target="_blank">
     <img alt="" src="https://assets.leetcode-cn.com/aliyun-lc-upload/uploads/2018/12/14/160_example_3.png" style="height: 126px; width: 200px;">
    </a>
   </p>
   <pre><strong>输入：</strong>intersectVal = 0, listA = [2,6,4], listB = [1,5], skipA = 3, skipB = 2
<strong>输出：</strong>null
<strong>输入解释：</strong>从各自的表头开始算起，链表 A 为 [2,6,4]，链表 B 为 [1,5]。由于这两个链表不相交，所以 intersectVal 必须为 0，而 skipA 和 skipB 可以是任意值。
<strong>解释：</strong>这两个链表不相交，因此返回 null。
</pre>
   <p>
    &nbsp;
   </p>
   <p>
    <strong>
     注意：
    </strong>
   </p>
   <ul>
    <li>
     如果两个链表没有交点，返回
     <code>
      null
     </code>
     .
    </li>
    <li>
     在返回结果后，两个链表仍须保持原有的结构。
    </li>
    <li>
     可假定整个链表结构中没有循环。
    </li>
    <li>
     程序尽量满足 O(
     <em>
      n
     </em>
     ) 时间复杂度，且仅用 O(
     <em>
      1
     </em>
     ) 内存。
    </li>
   </ul>
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